The concept of storage class memory (SCM) emerges recently, and this concept is based on next-generation non-volatile memory technology. Access effectiveness of the next-generation non-volatile memory is basically consistent with that of an ordinary memory module. Moreover, the next-generation non-volatile memory has the reliability of a semiconductor product, such as being shock-proof and compression-resistant. New data may be directly written to the next-generation non-volatile memory without erasing the existing data. Therefore, the next-generation non-volatile memory may be used as a next-generation storage device for alleviating a huge access speed difference between a processor and a storage. On one hand, like some conventional random access memories (RAM), an SCM may be directly hung on a memory bus, and directly face a central processing unit (CPU). On the other hand, functions of the SCM also extend to those of a conventional external storage, and may be used as a permanent data storage device.
It is predicted in the industry that, the next-generation non-volatile memories (NVMs) may become future storage devices to replace flash memories, magnetic disks or even dynamic random access memories (DRAMs). These storage devices have many excellent characteristics, such as fast access speed (close to that of a DRAM), addressable bytes (may be designed to have same access interface as that of a DRAM), and no lost data during a power failure (may persistently store data like flash memories or magnetic disks). By means of these characteristics, it is generally agreed that this type of innovative memory devices may become mainstream storage systems in a few years, and therefore results in revolutionary changes in the conventional storage system structure.
One of these revolutionary changes is that a file system may be residing in a memory, and it is intended to implement access to a file of the file system with data access performance approximate to that of an ordinary memory. Under this conceived architecture, use of a conventional file access manner becomes inappropriate.